Blood-corpuscles of A. tridactijlum, dee. By Dr. Schmidt. 71 
to be answered : What is the resisting force at the periphery which 
prevents it from escaping altogether if there exists no outer layer 
more consistent than the stroma itself? Sometimes the nucleus is 
observed to change its place suddenly by a certain start or jerk, 
while at the same time the whole blood-corpuscle rebounds to a 
little distance. This is another phenomenon difficult to explain 
upon the stroma theory, but easily accounted for in viewing the 
structure of the blood-corpuscle, such as I have described it above. 
The sudden displacement of the nucleus is caused by the contraction 
of the membraneous layer, over-distended by the expansion of the 
protoplasm, and occurs just at the time when the density of this 
substance has been rendered sufficiently low by the action of the 
water to allow the nucleus to move in it, and to leave its central 
position. In order to make the blood-corpuscle rebound, however, 
the weight of the nucleus must be greater than that of the rest of 
the corpuscles; and, besides, the contraction of the membraneous 
layer must take place unequally. 
Another phenomenon exhibited by the nucleated ellipsoidal 
blood-corpuscles of the Amphibia is that of assuming a round form, 
when treated in water ; it also has frequently been discussed and 
adduced for the purpose of either proving or disproving the 
existence of an enveloping membrane. Now in both cases it will be 
difficult to find a satisfactory explanation as long as we only keep 
in view the change of form which takes place in the main body of 
the blood-corpuscle. It seems to me more probable that the 
phenomenon originally depends on the dissolution of the granules 
in the interior of the nucleus; causing this body to swell and 
expand, and in consequence to assume a round form, which finally 
determines temporarily the form of the whole corpuscle. In 
accepting this explanation, however, the change of form in the 
nucleus itself, still remains to be accounted for. 
An interesting observation regarding the nucleus itself remains 
still to be mentioned. In a number of cases, during or after the 
escape of the nucleus, its delicate enveloping membrane, indicated by 
the fine double contour, bursts also, allowing the contents to exude. 
They generally escape in the form of a small spherical body 
(Fig. 23, a), which gradually enlarges as the process is proceedmg. 
Sometimes the escaping contents assume a more conical form, as 
represented at c. They are very pale, and bordered only by a 
delicate single contour. With the application of a very weak 
solution of chromic acid, this single contour becomes double, and is 
rendered much more distinct (Fig. 23, h). At the same time the 
double contour of the nucleus appears darker, and the contents 
within become finely granular. This change, of course, is caused 
by the action of the chromic acid, coagulating the surface of the 
escaping contents in the form of an artificial enveloping membrane. 
